1. Technical Field
The present invention relates to an optical disc. Particularly, the present invention relates to an optical disc with a thicker supporting section and a thinner recording section.
2. Description of the Prior Art
Optical discs, which are the most convenient storage media in the latest generation of optical storage market, can be used for storing data in various formats. They are broadly applicable in the fields of, for example, library archives, data backup, electronic publication, image data storage and personal medical record management.
Since the demand for the speed of data transmission is increasing, the effort is made on improving the reading/writing speed of optical disks. In the past, the rotating speed used was mostly not high, so issues due to high-speed rotation were usually ignored. However, under high-speed reading/writing, the deformation of the optical disc and the vibration during rotation become problems to which attention should be paid. The common sources of vibration of optical discs include, for example, air disturbance or poor balance of the optical disc itself.
In order to prevent optical discs from deforming under high-speed rotation, a conventional optical disc having a compensation sheet attached to the substrate is provided. In such configuration, it is necessary for the compensation sheet to be aligned with the substrate before being attached thereto. Thus, the complexity and difficulty of the process for manufacturing optical discs increase, and so does the material cost of the compensation sheet. In view of this, Taiwanese Patent No. 1267847 has disclosed an optical disc (hereinafter, Patent Disc 1), in which the thickness of the superimposed supporting section and protruding section is greater than that of the recording section, so that Patent Disc 1 can be directly held by an optical disc drive. Thus, an additional compensation sheet as that in the conventional optical disc is not necessarily provided to thicken the optical disc for facilitating the holding of the optical disc drive. This can result in a reduced cost for manufacturing optical discs. However, the problems of deformation and vibration as shown in FIG. 1 are more likely to occur during operation. In FIG. 1, the structural strength of an optical disc 10 (represented by lines) itself is insufficient. As the optical disc rotates, since the resonant frequency thereof is too low, vibration indicated by the vertical arrow happens easily, resulting in difficulties in the focusing of the laser read/write head. In order to solve the problem of vibrations of optical discs, several techniques such as those described below have been developed for reinforcing the structure of optical discs.
Taiwanese Patent No. 1322417 has disclosed an optical disc (hereinafter, Patent Disc 2), in which the included damping layer can reduce the vibration affecting time of the optical disc, thereby resolving reading/writing problems due to vibrations at various speeds resulting from insufficient thickness or rigidity.
Nevertheless, since the recording portion of the annular substrate of Patent Disc 2 is thin (e.g. between 0.55 mm and 0.65 mm), as the coating layer and/or the damping layer attached to the recording portion contract during the optical disc manufacturing process due to the material properties thereof, the recording portion of the annular substrate becomes warped and deformed toward the side where the coating layer and the damping layer are disposed, which may cause the optical disc to lose its capability of being read/written. Therefore, to solve this problem, Taiwanese Patent No. 200910342 provides a read-only or writable DVD optical disc with thick supporting section and thin recording section (hereinafter, Patent Disc 3), which comprises a reinforced structure for reducing vibrations, and a rectification layer for rectifying disc deviation in fabricating process.
By comparing the abovementioned conventional optical discs, Patent Disc 1 is advantageous in material-saving and requiring no attachment, while it can only be used for a lower reading/writing speed ranging from 1× speed (maximum: 1500 rpm approx.) to 4× speed (maximum: 6000 rpm approx.); the reading/writing speed of Patent Disc 2 and Patent Disc 3 meets the requirement for more than 16× speed (9300 rpm approx.), while the defects such as greater material requirement and complex fabricating process still exist therein.